Cathode ray device



Dec. 28, 1937, M. c. BANCA 2,103,312

CATHODE' RAY DEVICE Filed Aug. 29} 1953 INVENTOE j qa g lloflliwwmPatented bee. 28, 1937 OATHODE RAY DEVICE Mugio C. Banca, Magnolia, N.J., assignor to RadidCor-poration of America, New York, N. Y.,

.a corporation of Delaware Application August 29, 1938, Serial No.687,298

9 Claims. My invention relates to improvements in television systems.

In television systems embodying a cathode ray tube at the transmittingstation, and in which the tube comprises a photo-sensitive mosaic screenon which an image of the object is projected, and which is has beenfound to be advantageous to project the image on the same side of thescreen which is scanned by the ray. When this is done, the axis of theoptical system for projecting the image is usually made perpendicular tothe screen, but the axis of the so-called gun for developing anddirecting the ray of electrons is, for convenience, disposed at an angleto the screen. On account of this arrangement, the outline of the areascanned by the ray has a keystone shape rather than the desiredrectangular shape. This distortion of the scanned pattern is manifestedby a substantial and corresponding distortion ofthe reproduced image atthe receiving station, the

reproduced image being'also the shape of a keystone, with the verticallines inclined down- I wardly toward each other.

With the foregoing in mind, it is one of the objects of my invention toprovide an improved television systemof the character referred towherein the keystone distortion is corrected.

Other objects and advantages will hereinafter appear.

In accordance with my ray at the transmitting station is deflected insuch manner as to tend to spread out the scanned pattern in a keystoneeffect opposite to the keystone pattern which would otherwise bescanned, the effect being to substantially entirely com-. ,pensate orcorrect for the latter, so that the scanned pattern is rectangular inshape.

. More particularly, in accordance with my invention, complementaryplates are usedto deflect the cathode ray at the higher frequency,sometimes referred to as the line frequency. These plates are tiltedwith respect to each other in such manner and amount to cause theamplitude of deflection to vary uniformly during each scanning period.In this way, each line is made slightly shorter by thesame amount fromeach end thereof than the preceding line, to cause the ray to scan akeystone area in a plane perpendicular to the tube axis, the sides ofthisarea being Y inclined upwardly toward each other. when the raystrikes the inclined screen, therefore, and is deflected in the twodirections at right angles invention, the cathode to each other, it iscaused to scan the screen over a rectangular area.

scanned by a cathode ray, it

(c1. est-21.5)

My invention resides in the improved apparatus of the characterhereinafter described and. claimed, For the purpose of illustrating myinvention, an embodiment thereof is shown in the drawing, wherein YFigure 1 is a perspective view, partly diagrammatic, ofatransmittingtube constructed and operating in accordance .with my invention;

Fig. 2 is a simplified, front elevational view, taken from Fig. '1;

Fig.3 is a plan view of Fig. 2; y

Fig. 4 is a sectional view, the section being taken on the line 4-4 inFig. 2; and

Fig. 5 is a diagrammatic view illustrative of the principle ofoperation.

face l4 comprised of a great number of minute metallic elements, such assilver globules, each insulated from the electrode [2 and from eachother, and each provided with a coating of photosensitive material. Inoperation, an image of the object, shown as being in the form of amoving picture film tivesurface by a suitable optical system H, the axis18 of the optical system being perpendicular to the screen surface It. Mr

A gun 20 of any suitable construction operates to develop and thephotosensitive surface I, the axis 22 of the gun being disposed at anacute angle, for example to the photosensitive surface I4.

For the purpose of causing the ray to scan the photosensitivesurface ofthe screen 12, a

saw-tooth voltage wave at a frequency of 24 cycles, for example, isapplied across complementary plates 26, and a saw-tooth voltage wave ata frequency of 4320 cycles, for example, is applied across complementaryplates. 28. The ray, therefore, isdeflected vertically 24 times a second.by the plates 26, and is simultaneously deflected horizontally 4320times a second by the plates 28. The plates 26 and 28 are disposedwithin the tube, as represented, and may be carried by supportingelements (not shown) extending from the struc-' ture of the gun 20. r

\ Inoperation, the projection of the image on the photosensitive surfaceit causes discrete electrostatic charges .to'be-stored up over thesurface, each elemental charge being proportionate to the lightintenslty at the elementalarea. As the ray 24 scans the surface l4,these charges are neutralized to develop picture signals which are InFig. 1, a transmitting tube I0 is provided with an electrode i2 having aphotosensitive sur-v IB, is projected upon the photosensidirect a my 24of electrons at.

supplied to a radio or tem (not shown).

Ordinarily, the ray 24 would scan the surface l4 over an area ABCD, asshown in Fig. 5. That is, the scanning pattern would be the shape of akeystone rather than the desired rectangle. This would cause, at thereceiving station, the production of a distorted image on thefluorescent screen of the usual cathode ray tube, the vertical lines ofthe reproducedimage being so inclined to each other that the entireimage would have a generally keystone configuration.

For the purpose of compensating or correcting for the keystonedistortion referred to, I propose to position the plates 28 in thefollowing manner. These plates are on opposite sides of the axis 22' ofthe tube, and diverge upwardly from each other, as more clearly shown inFig. 4, the lower edges 28a being, therefore, substantially closertogether than the upperedges 28b, the edges 28a being on the same sideof the tube axis 22 as the lower edge |2a of the screen which is nearerto the gun 20.

For the purpose of providing clearance for full horizontal deflection ofthe ray between the two extreme positions W and X, the plates 28 arealso made to diverge outwardly from each other in the direction lookingtoward the screen l2, as more clearly shown in Fig. 3. The edges 280,which are nearer to the gun 20 are, therefore, closer together than theedges 28d.

Likewise, for the purpose of providing clearance for full verticaldeflection of the ray between the two extreme positions Y and Z, theplates 26 are made to diverge outwardly from each other in the directionlooking toward the screen l2, as more clearly shown in Fig. 2. The edges260 of the plates, which are nearer to the gun 20, are therefore closertogether than the edges 26d.

In operation of the tube, asthe ray isdeflected horizontally andsimultaneously deflected vertically downward the amplitude of anyhorizontal deflection is slightly greater than the amplitude of thepreceding horizontal deflection. The ray 24, therefore, is caused toscan a keystone area such perpendicular to the axis 22 and which isabout the same distance from the gun 20 as the screen l2. The result isthat the ray scans the screen I2 over the desired rectangular area suchas is represented in Fig. 5 by the area JKLM.

The action just described is attributed to the fact that, for the sameconditions of voltage, the amplitude of deflection of a cathode ray byplates is inversely proportional to the average distance between theplates where the ray is. at the instant. It will, therefore, be apparentthat when the ray is between the upper edge portions of the plates 28the amplitude of horizontal deflection will be a minimum, and when theray is between the lower edge portions of the plates the amplitude ofhorizontal deflection will be a maximum.

In the drawing, the center of the screen I2 is considered to besubstantially eight inches from the tip of the gun 20, and to beinclined 60 to the axis 22. With regard to the respective angles ofinclination of the plates 28 and 28', these are determined according tothe various dimensions and requirements of any particular tube. In theparticular tube shown,-satisfactory results have been obtained with therespective angles about as shown and designated.

' Fora receiving tube, the embodiment of my invention would be the sameas in the transmitting tube disclosed, but the front-surface ofthescreen other transmitting sysas EFGH in Fig. 5, in a plane l2 would becoated with fluorescent material, and

the optical system I! would be one which would project onto a relativelylarge, external screen, the image reproduced on the fluorescent screen.

From the foregoing it will be seen that I have provided improved cathoderay apparatus wherein the screen is inclined substantially to the axisof the tube, and wherein the ray is caused to scan the screen over asubstantially rectangular area by the action of at least one pair ofplates which deflect the ray at the higher line-frequency. In thisconnection, it will be understood that electromagnetic coils can be usedinstead of the plates 26 for deflectingthe ray at the lower orframefrequency.

While but one embodiment of my invention has been described, it will beunderstood that various modifications are possible without departingfrom the spirit of my invention or the scope of the claims.

I claim as my invention:

1. A cathode ray device comprising, screen structure, means for scanningsaid structure comprising means for developing a scanning ray anddirecting the same at said structure, the axis of said ray-developingmeans being inclined at an acute angle to said structure, and means fordeflecting said ray simultaneously in different directions at relativelyhigh and relatively lowfrequencies respectively to cause the ray to scansaid structure over a substantially rectangular area, said deflectingmeans including complementary non-parallel plates disposed on oppositesides of said axis for deflecting the ray at the relatively highfrequency.

2. A cathode ray device comprising a tube provided with a substantiallyflat screen and with means for developing a scanning ray and directingthe same at said screen, the axis of said ray- .develo'ping means beinginclined at an acute angle to said screen whereby the part of the latteron one side of said axis is closer to said raydeveloping means than theother part of said screen, and means for deflecting said raysimultaneously in different directions at relatively high and relativelylow frequencies respectively to cause the ray to scan said screen over asubstantially rectangular area, said deflecting means includingcomplementary non-parallel elements disposed on opposite sides of saidaxis for deflecting the ray at the relatively high frequency andinclined to each other in the direction to cause said elements toconvergetoward each other on said one side of said axis.-

3. A cathode ray device comprising atube provided with a substantiallyflat screen and with means for developing a scanning my and directingthe same at sa developing means. being inclined at an acute angle tosaid screen whereby the part of the screen, the axis of said raylatteron one side of said axis is closer to said raydeveloping means than theother part of said screen, and means for deflecting said raysimuldirections at relatively high taneously in different and relativelylow cause the ray to scan tially rectangular area, said deflecting meansincluding complementary plates for deflecting the ray at the relativelyhigh frequency and disposed within the tube on'opposite sides of saidaxis, said plates being disposed in non-parallel planes frequenciesrespectively to and inclined to each other in directions to cause saidscreen over a substan-' said plates to converge toward each other onsaid one side of-said axis.

4. A cathode ray device comprising a'tube pro aioasia F v 1 'vided witha substantially flat screen and with means 101- developing a scanningray and directingthe same at said developingmeans being inclined to saidscreen at an acute angle of the order of sixty degrees whereby the axisis closer to said ray-developing means than the other part-oi saidscreen, and means for deflecting said ray simultaneously in diflerentdirections at relativelfhigh andrelatively low frequencies respectivelyto cause the ray to scan said screen over a substantially rectangulararea, said deflecting means including a pair of plates for deflectingthe ray atthe relatively highdrequency and disposed within the tube onopposite sides of said axis-said plates being disposed in non-parallelplanes directions to' cause said plates to converge toward each other onsaid one side of said axisan'd to verge from each other in the directiontoward said screen.

5. A cathode ray device comprising a tube provided with a substantiallyflat screen and with means tor-developing a scanning ray and directingthe same at said screen; the axis of said ray-developing means beinginclined to said screen at an acute angle or the order of sixty degreeswhereby the part oi said screen on one side of said axis is closer tosaid ray-developing means than the other part c! said screen, means fordeflecting said ray simultaneously in dinerent directions at relativelyhigh and relatively low frequencies respectively to cause the ray toscan v said screen over a substantially rectangular area,

said-deflecting means including a pair of plates for deflecting the rayat the relativellh l irequency and disposed within the tube on oppositesides of said axis, said plates being disposed in non-parallel planesand.incli ned to each other in directions to cause said plates toconverge toward each otheron said one side of said axis and to divergefrom each other in the direction to'- ward said screen. and a secondpair otplates 1 dis osed between said ray-developing means and .saidfirst pair of plates for deflecting the ray at the relatively lowireduency. the plates of said second pair being disposed withinsaid-tube on opposite sidesoi said .axisand in non-parallel planes andinclined to each other in directions to cause said plates to divergefrom each the direction toward screen.

. 6. A cathode ,ray de ce I comprising screen istructure',meansiorscanningsaidstructurecomprising means for developinga scanning ray and 5; directingthesam eatsaidstructuratheaxi'sor screen.the axis of said raypart of said screen on oneside of said and inclinedto each other in' r in l intersecting planes, the line oi intersectionof the said ray-developing'means being inclined atwan acute angle tosaid structure, and means ior de-' flecting' said ray simultaneously indiflerent directions at relatively high and relatively low freduenciesrespectively to cause the ray to scan said structure over asubstantially rectangular ,said deflecting means including complementaryplates disposed in intersecting planes and on opposite sides of saidaxis for deflecting the ray at the relatively high frequency.

'1. A cathode ray device comprising screen structure, means for scanningsaid structure comprising means for developing a scanning ray anddirecting the same at said structure, the axis of said ray developingmeans being" inclined at an acute angle to said structure, andpairss'oi,

plates for deflecting said ray simultaneously in dliierent directions atrelatively ,high and .reladisposed in intersecting planes 8. A cathoderay device comprising screen structure, means for scanning saidstructure comprising means for developing a scanning ray and directingthe same at said structure, the axis of said ray-developing meansbeinginclined at an acute angle to said structure, and means for deflectingsaid ray-simultaneously in diflerent directions at relativelyv high andrelatively low frequencies respectively to cause the ray to scan saidstructure over a substantially rectangular area, said deflecting meansincluding complementary' plates disposed on opposite sides oi said axisfor deflecting the ray at the relatively high frequency, said platesbeing disposed in intersecting planes wherein the line oi'intersectionthereof intersects a line parallel to the tube axisat an angle lessthanninety degrees. r 9. A cathode ray device comprising screenstructure,.means for scanning said structure.

comprising means for developing a scanning ray and directing the same atsaid structure, the axis ot ,said ray-developingmeans being inclinedat'an for deflecting said ray simultaneously in different directions atrelatively high and relatively low finite angle to said structure,- andpairs of plates 1 frequencies respectively to cause the my to scan saidarea, the platesot each pair being disposed in planes in which one pairof plates lies intersecting a line parallel to-the tube axis at an angleless than ninety degrees. f v v MAGGIO C. BANCA.

Etna-tine over a substantially rectangular

